This section is intended to introduce various aspects of the art, which may be associated with exemplary embodiments of the present techniques. This discussion is believed to assist in providing a framework to facilitate a better understanding of particular aspects of the present techniques. Accordingly, it should be understood that this section should be read in this light, and not necessarily as admissions of prior art.
The extraction and transport of petroleum from a reserve or reservoir often involves movement of petroleum through one or more lengths of pipeline. Petroleum comprises a hydrocarbon fluid mixture that can include, as examples, various concentrations of light hydrocarbons and wax, as well as non-hydrocarbon compounds. The mixture is sometimes referred to as a waxy crude.
Movement of waxy crudes through a pipeline faces a number of challenges. One challenge is that as the temperature of the waxy crude decreases, the associated fluids can exhibit complex rheological properties at lower than the wax appearance temperatures. In these temperatures, wax begins to crystallize and can interlock with itself and other suspended solids. As the temperature decreases further, the fluid approaches the pour point temperature and will form a gel or gel-like substance. That is, the fluid can go from acting as a simple Newtonian fluid to a complex viscoelastic and thixotropic fluid. Once the fluids approach the pour point temperature, the fluids can exhibit large yield stresses and additional viscous components.
While gelling during operation is a concern due to increased apparent viscosities, perhaps a bigger concern is gelling during shut-in scenarios. If the fluid is allowed to gel while stagnant, the pressures needed to overcome the yield stress and restart the pipeline can be substantial. In some cases the required pressure can exceed the maximum allowable pressure of the piping. One consequence is that if the corresponding production facility does not have enough well head pressure, or pumping pressure, to restart a gelled pipeline, the end result may be that no more fluid can be passed through the pipeline.
In conventional petroleum transport, there are two ways to compensate for gelling in pipelines. One way is to add chemicals, sometimes referred to as pour point depressants, to the fluid. These added chemicals interact with the wax structure that is formed and weaken it reducing the strength of the gel. However, these chemicals can lead to significant operational expenditures. A second way to compensate for gelling in pipelines is to heat the pipelines to keep the temperature of the fluid from going below the pour point temperature. However, the amount of heat required can be significant, especially during a shut-down for an indefinite amount of time, resulting in significant operational expenditures, in addition to capital expenditures for high-capacity heating equipment. Thus, there is a need for less-costly alternatives for treating petroleum products, including waxy crude, that might assist with re-starting gelled pipelines, particularly during shut-in scenarios.